Communication network using different transmission properties

ABSTRACT

In an ATM communication network ATM cells to be transmitted from a terminal device ( 46 ) to a network control node ( 12 ) are transmitted according to certain transmission properties also called Quality of Service. In order to determine the Quality of Service with which a given packet has to be transmitted, the Quality of Service is determined from address information in the VPI/VCI identifier in the header of the ATM cell. In an embodiment of the invention a network termination ( 32 ) comprises address translation means ( 76 ) for translating the address present in ATM cells received from the terminal device ( 46 ) into addresses indicating the Quality of Service.

BACKGROUND OF THE INVENTION

The present invention is related to a communication network comprising aplurality of secondary nodes being coupled to at least one primary node,said secondary nodes being arranged for transmitting packets to theprimary node according to predetermined transmission properties.

The present invention is also related to a node for use in such acommunication network and a communication method.

A communication network according to the preamble is known from theconference paper “A Hybrid Multiplexing Scheme for Multi-ServiceNetworks” published in the proceedings of SPIE conference on BroadbandAccess Networks, Vol. 2917, Boston, November 1996.

There is an increasing interest in switched broadband networks to offervarious services to subscribers connected to such networks. Possibleservices are Broadcast TV, Video on Demand, Video conferencing,telephony and fast Internet access. One of the most promising solutionsfor realizing such a network is a so-called Hybrid Fiber Coax (HFC)network. Standardization of these broadband networks is done inIEEE802.14, DVB and DAVIC.

In order to provides services having quite different properties suchnetworks can be based on ATM. In ATM the information to be transmittedis subdivided in fixed length packets with a 5 byte header and a 48 bytepayload area. In ATM the possibility exists to transmit different typesof packets (audio, video and data) using different transmissionproperties, also called Quality of Service types. For real time videocommunication, a high bit rate and a low delay are required. For videobroadcast a high bitrate is required, but some delay can be tolerated.In both cases a Constant Bit Rate connection is required, each withdifferent delay requirements. For real time audio transmission thebitrate can be lower, but the delay requirements are substantially thesame. For data communication such as file transfer a lower bitrate canbe tolerated, and almost no delay requirements have to be fulfilled.

In the above mentioned prior art document it is not disclosed how therequired transmission properties are associated with packets to betransmitted to the primary node.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a communication networkaccording to the preamble in which the required transmission propertiesare associated in an easy way with the packets to be transmitted to theprimary node.

To achieve said object, the communication network according to theinvention is characterized in that the secondary node comprisesselection means for selecting packets according to address informationin their header, and in that the transmission means are arranged fortransmission of said packets with transmission properties dependent onthe selection performed by the selection means.

By selecting packets according to their address information andassigning transmission properties according to said address information,the transmission properties are associated with the packets to betransmitted in an easy and effective way.

An embodiment of the communication network according to the invention ischaracterized in that in that the secondary node comprises addresstranslation means for translating initial address information carried bypackets received from at least one terminal device into said addressinformation carrying information about the transmission properties to beused for transmitting the associated packets.

This embodiment of the communication network allows it to be interfacedto terminal devices which are being addressed in a standard way. Thisstandard way can be the way terminal devices are addressed in a publicATM network. By translating the standard address into an addresscomprising information about the transmission properties to be used, theterminals can still be identified in a standard way. The addressassigned to a secondary terminal in such a core network is translatedinto an address suitable for use in the network according to theinvention. By identifying the transmission resource by a first part ofthe address information, the signal can be directed into the proper partof the network. The second part of the address information can be usedto direct the further routing in the network.

A further embodiment of the communication network according to theinvention is characterized in that the communication network comprisesfurther address translating means for translating said addressinformation back into the address information present in the packetsreceived by the secondary nodes from said terminal device.

By introducing additional address translating means for translating thetranslated address part back into the address information present in thepackets received from the terminal devices, it is obtained that thecommunication network according to the invention is fully transparentbetween the input of the secondary node and the output of the primarynode.

A further embodiment of the communication network according to theinvention is characterized in that the communication network comprisescross connect means for passing packets from the secondary nodes to anoutside network, and in that the further address translating means arearranged for translating the address information before the packets areapplied to the cross connect means.

By positioning the further address translation means between a crossconnect and the rest of the network, the network specific addressinformation can be used in the complete network except the connectionsto a core network and the connections to the terminal units.

BRIEF DESCRIPTION OF THE DRAWING

The invention will now be explained with reference to the drawings.Herein shows:

FIG. 1 a communication network in which the invention can be applied;

FIG. 2 the downstream elements in a communication network according tothe invention;

FIG. 3, a diagram explaining the address translations to which an ATMcell is subjected when it is transmitted from the core network 2 to theterminal 46;

FIG. 4, the upstream elements in a communication network according tothe invention;

FIG. 5, a diagram explaining the address translations to which an ATMcell is subjected when it is transmitted from the terminal 46 to thecore network 2;

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The communication network according to FIG. 1 comprises an accessnetwork 1 which is connected to a core network 2 via a switch 4. Theaccess network comprises a plurality of service areas 21, 23 and 25. Theswitch 4 is coupled to said service areas 21, 23 and 25 via across-connect 8. Each of the service areas 21, 23 and 25 comprises acorresponding Network Control Node 3, 12 and 5 respectively. The networkcontrol nodes 3, 12 and 5 are coupled to a HFC network which normallycomprises a shared transmission network 7, 9 and 19 such as a CATV coaxnetwork.

The Network Control Nodes transform the signals received from the crossconnect 8 into signals modulated on separate carriers for transmissioninto the corresponding HFC network. In the HFC network a number ofcarriers e.g. 128 are available for transmission signals to thesecondary nodes, being here network terminations (NT) One of thesenetwork terminations 11 is drawn in FIG. 1. Each NT is arranged forreceiving one of said carriers used in the HFC network. The networktermination 11 is arranged for passing the signals received from the HFCnetwork to the terminal devices 13, 15 and 17. In each service area thesame carrier frequencies can be used because there is no connectionbetween the HFC networks of different service areas.

The network terminations 11 and 32 are arranged for passing signals fromtheir terminals 13, 15, 17 and 46, 48 respectively via an upstreamcarrier via the HFC network 7, 9 to the corresponding Network ControlNode 3, 12. In order to be able to use the HFC network for upstreamtransmission an access protocol such as described in IEEE 802.14, DVB orDAVIC should be used.

In FIG. 2, the downstream elements used in the network according to FIG.1 are drawn in more detail. The core network 2 is a public broadbandnetwork which can be based on ATM. The switch 4 is arranged for settingup connections between subscribers connected to the core network andsubscribers connected to the access network 1. The switch 4 is alsoarranged for setting up local connections between subscribers bothconnected to the access network 1. The address information contained inthe ATM cells entering and leaving the switch 4 is according to theaddressing scheme used on the core network 2.

The switch 4 is further connected to a cross-connect 8 which is arrangedfor directing the ATM cells into the proper parts in the access network.In order to enable the cross connect to direct the ATM cells to theproper parts of the network, at an interface P10 the address of the ATMcell is translated by the further translation means, being here atranslator 6. The address carried by ATM cells at the input of thetranslator 6 is translated into an address comprising a VPI identifieridentifying the service area to which the cell should be routed andwhich carrier should be used in said service area. This translation isperformed by reading a table which is addressed with the originalVPI/VCI identifier of the ATM packet.

The table in translator 6 is updated each time a connection is set up oris disconnected. During the set up of a call a table entry with inputvalue the VPI/VCI identifier of the terminal to be called is added. Thecorresponding output value comprises information about the service areaand the carrier to be used in the VPI field, and an identification ofthe terminal to be addressed in the VCI field.

The cross connect 8 reads the VPI field of the incoming ATM packets, androutes it to an output determined by the VPI value. All outputs of thecross connect 8 are passed to the address translating means according tothe inventive concept, being here an address translation unit 10. Theaddress translation unit 10 replaces the combination of VPI/VCI by a newcombination of VPI/VCI which is determined from the original VCI valueonly. This translation enables a more flexible addressing, because alarger address space is available.

In the new combination of VPI/VCI, the VPI field is used to address thenetwork terminator to which the destination terminal is connected. TheVCI field identifies the destination terminal.

The ATM packet with the translated address information, is passed via amultiplexer 14 to a modulator in the service area having a predeterminedcarrier frequency. The selection of the service area and the modulator(is selection of carrier frequency) therein is done on basis of theoutput VPI value at interface P10. The multiplexer 14 is present toenable the Network Control Node 12 to transmit control information tothe corresponding Network Termination. The output signal of the selectedmodulator (e.g. 22) is combined with the output signals of the othermodulators (e.g. 22 and 26) and transmitted via the coax network 28 tothe network terminations 30, 32.

The network terminations 30, 32 demodulate and process the signalreceived at the carrier frequency assigned to them. In the networktermination 32 a demodulator 42 demodulates the signal received from theHFC network 28. A demultiplexer 42 connected to the demodulator 40extracts control information intended for control of the NetworkTermination 32. A plurality of outputs of the demultiplexer 42 isconnected to the additional address translating means, being here anaddress translator 44. This address translator 44 translates the VPI/VCIcombination introduced by the address translator 10 into the addressesas they were received from the core network. Subsequently the packetsare transmitted to the terminals 46 and 48.

If the VPI field is 12 bits and the VCI is 16 bits as is the case forATM cells for use on Network Node Interfaces 12 bits are available foridentifying the Service Area and the carrier frequency to be usedtherein. If the network comprises 32 service areas, 128 carrierfrequencies can be defined. For each of the service areas 12 bits areavailable for identifying the network termination and 16 bits areavailable for identifying the terminal. Consequently 4096 networkterminations and 65536 terminals can be addressed in each service area.

Without the address translation at interface P10, 16 bits would beavailable for addressing the network terminations and the terminals. Ifin such a case 4096 NT had to be addressed, only 16 terminals could beselected with the remaining address space. Consequently only 16terminals could be connected to one Network Termination. By using theaddress translation according to the invention 65536 terminals can be ina connection, without any constraint to the network termination they areconnected to.

FIG. 3 shows the sequence of address translation to which an ATM packetis subjected when traveling from the core network to a terminal. Apacket from the core network 2 has a VPI/VCI part 31 as is shown in FIG.3. At the interface P10 this VPI/VCI part is translated into aVPI_(C)/VCI′ part 35. This translation is performed by addressing atable 33 with the VPI/VCI part as input signal and reading theVPI_(C)/VCI′ part from the output of the table 33. The table 33 is heldby the translation means 6 in FIG. 2. As can be seen in FIG. 3 thecomplete address information VPI/VCI is used for addressing the table33.

The VPI_(C) part of the address information 35 is used to route the ATMpacket to the proper service area and modulator. The VCI′ part of theaddress information is used as input for the translation of the addressinformation at interface P7. The VCI′ part is used to address a table 37from which the translated address information VPI_(NT)/VCI″ is read. Thetable 37 is held in the translation means 10 in FIG. 2. The partVPI_(NT) indicates the address of the NT to which the destinationterminal is connected, and the part VCI″ indicates the address of thedestination terminal.

The combination 39 of the address information VPI_(NT)/VCI″ is used asinput for the address translation at interface P2. Said combination ofVPI_(NT)/VCI″ is used to address a table 41 which is held in thetranslator 44 in FIG. 2. At the output of the table the VPI/VCIcombination according to the addressing scheme of the core network isavailable for addressing the terminal.

FIG. 4 shows the elements involved with the upstream transmission for acommunication network according to FIG. 1. An ATM packet originated at aterminal 46 or 48 is applied to an address translator 76. The addresstranslator 76 in the network termination 32 translates the originaladdress information VPI/VCI into translated address informationVPI_(NT)/VCI_(PRIOR).

The part VPI indicates the Network Termination 32 via which the packetis transmitted. According to an aspect of the present invention, thepart VCI_(PRIOR) indicates the Quality of Service with which the ATMpacket has to be transmitted. The selection means being here a selector74, selects the ATM packets received from the translator 76 and passesthem to one of the buffers 68, 70 or 72 according to their VCI_(PRIOR)indicator. The buffer 68 can be assigned to a Constant Bitrate QoS (CBR)with a high bitrate, the buffer 70 can be assigned to a Constant BitrateQoS (CBR)with a medium bitrate, and the buffer 72 can be assigned to aVariable Bitrate (VBR) QoS.

A CBR QoS with high bitrate is e.g. suitable for transmission of videosignals, a CBR QoS with medium bitrate is e.g. suitable for transmissionof audio signals, and a VBR QoS is suitable for the transmission of datawhich occurs e.g. with file transfer. The ATM packets at the output ofthe buffers 68, 70 and 72 are multiplexed with a multiplexer 64 into anoutput stream. The multiplexer takes the different QoS properties of theoutput signals of the buffers 68, 70 and 72 into account, bytransmitting the packets according to a priority which is dependent onthe buffer from which the packet is read. It is clear that the bufferscarrying CBR signals have a higher priority than the buffers carryingVBR signals. Amongst the buffers carrying CBR signals, the buffersassigned to high bitrate streams have the highest priority. Besides thesignals from the buffers 68, 70 and 72, also a control signal from thenetwork termination 32 is applied to an input of the multiplexer, inorder to be transferred to the network control node 12.

The output signal of the multiplexer 64 is modulated by a modulator 62on a carrier with a frequency which is assigned to the networktermination 32. The transmission means according to the inventiveconcept comprises the combination of the multiplexer 64 and themodulator 62. The network termination 32 transmits the output signal ofthe multiplexer 62 via the network 28 to the network control node 12. Inthe network control node, the signal received is demodulated in one ofthe demodulators 56, 58 or 60 and demultiplexed by a correspondingdemultiplexer 50, 52 or 54. The control information from the networktermination 32 is available at a separate output of the demultiplexerfor further use in the network control node 12.

The outputs of the demultiplexers 50, 52 and 54 are connected tocorresponding inputs of an address translator 10. This addresstranslator translates the combination of VPI_(NT)/VCI_(PRIOR) into newaddress information VPI_(OUT)/VCI′. This translation is obtained byreading a table entry using the VCI_(PRIOR) indication as entry. The ATMcells at the output of the address translator 10 are passed by thecrossconnect 8 to one of its outputs according to the VPI_(OUT)indicator of the ATM packet. The outputs of the cross connect 8 areconnected to corresponding inputs of address translation means 6. Theaddress translating means 6 translates the combination of VPI_(OUT)/VCI′into the original destination address VPI/VCI of the packet. The packetwith the original address VPI/VCI is transferred to the switch 4 inorder to transmit the packet to the core network 2.

FIG. 5 shows schematically the sequence of address translation to whichan ATM packet is subjected when traveling from a terminal 46 or 48 tothe core network. A packet from the terminal 46 or 48 has a VPI/VCI part43 as is shown in FIG. 5. At the interface P2 this VPI/VCT part istranslated into a VPI_(NT)/VCI_(PRIOR) part 47. This translation isperformed by addressing a table 45 with the VPI/VCI part as input signaland reading the address information VPI_(NT)/VCI_(PRIOR) from the outputof the table 45. The table 45 is held by the translation means 76 inFIG. 5. As can be seen in FIG. 5 the complete address informationVPI/VCI is used for addressing the table 45.

The VCI_(PRIOR) part of the address information 47 is used to route theATM packet to the Network Control Node 12 via a path being able toprovide transmission according to the proper Quality of Serviceindicated by the address part VCI_(PRIOR). The VCI_(PRIOR) part of theaddress information is used as input for the translation of the addressinformation.

At interface P7, the VCI_(PRIOR) part of the address information 47 isused to address a table 49 from which the translated address informationVPI_(OUT)/VCI′ is read. The table 49 is held in the translation means 10in FIG. 4. The part VPI_(OUT) indicates the output of the cross connect8 to which the packet should be transferred.

The combination 51 of the address information VPI_(OUT)/VCI′ is used asinput for the address translation at interface P10. Said combination ofVPI_(OUT)/VCI′ is used to address a table 53 which is held in thetranslator 6 in FIG. 5. At the output of the table 53 the VPI/VCIcombination according to the addressing scheme of the core network isavailable for submitting the packet to the switch 4.

It is observed that the address translation at the interfaces P10, P7and P2 are very similar for upstream and downstream. This enables thatthe translation units 6, 10 and 76 can be used for downstream andupstream traffic.

What is claimed is:
 1. Communication network comprising: a plurality ofsecondary nodes being coupled to at least one primary node, thesecondary nodes being arranged for transmitting packets to the primarynode according to a plurality of predetermined transmission properties,characterized in that the secondary node comprises: a first addresstranslator that is configured to translate initial address informationcarried by packets received from at least one terminal device intoaddress information in headers of the packets comprising informationabout transmission properties to be used for transmitting the associatedpackets, a selector that is configured to select packets according tothe information about the transmission properties contained in theaddress information in their header, a transmitter that is configured totransmit each of the packets with one or more transmission properties ofthe plurality of predetermined transmission properties corresponding tothe selection performed by the selector, and the network furtherincludes a second address translator that is configured to translate theaddress information in the packets received from the secondary node backinto the initial address information present in the packets received bythe secondary nodes from the terminal device.
 2. Communication networkaccording to claim 1, characterized in that the primary node comprisesthe second address translator.
 3. Communication network according toclaim 1, further comprising a cross connect switch that is configured topass packets from the secondary nodes to an outside network wherein thesecond address translator is configured to translate the addressinformation before the packets are applied to the cross connect switch.4. Node for use in a communication network, the node being arranged fortransmitting packets according to a plurality of predeterminedtransmission properties to a primary node, characterized in that thesecondary node comprises selection means for selecting packets accordingto address information in their header, transmission means that arearranged for transmission of the packets with one or more transmissionproperties of the plurality of transmission properties dependent on theselection performed by the selection means, and address translationmeans for translating initial address information carried by packetsreceived from at least one terminal device into the address informationcarrying information about the transmission properties to be used fortransmitting the associated packets, wherein the primary node isconfigured to translate the address information back into the initialaddress information present in the packets received by the secondarynodes.
 5. Communication method comprising: translating initial addressinformation carried by packets received from at least one terminaldevice into address information in the header of the packets, theaddress information comprising information about transmission propertiesto be used for transmission of the associated packets, selecting packetsaccording to the information about the transmission properties containedin the address information in their header, transmitting the packetsfrom a node with one or more transmission properties of the plurality ofpredetermined transmission properties corresponding to the selectionperformed, receiving the packets at an other node, and translating theaddress information from the packets that are received at the other nodeback into the initial address information present in the packets fromthe at least one terminal device.